how can we know that it is astrong field or weak field ligand

actually knowing a weak and strong field ligand is done by cristal field splitting theory . but here is a trick for it 

use ( kan nak aur hath) ( kan= carbon containing ligand, nak= nitrogen cont, aur= oxygen cont , hath= halogen cont) among these first two are strong and other two are weak ligand . use this u will definetely get correct answer. thank u